The models proposed in [1]}, [2]} differ from the GTG model described above (which follows [3]}) in that the response generation in [1]}, [2]} is performed in two steps, following the classical pipeline architecture (Figure REF ) where action selection using dialog policy (POL) and natural language generation (NLG) are performed by two separate modules.
Instead of generating \(Y\)  directly from \((c, b, s)\)  as in Equation REF , system action \(a\)  is first generated based on \((c, b, s)\) , and delexicalized response \(Y\)  is generated based on \((c, b, s, a)\)  as:
\(a=\text{GTG}(c,b,s)\) 
